Railway Science (Physics-Light and Optics) (Part-V)

Total Questions: 50

11. Which of the following cannot be used for making lenses? [RRB Group D 17/09/2018 (Afternoon)]

Correct Answer: (b) Soil
Solution:

Soil - It is an opaque material and light cannot pass through it. Lenses are made of transparent material (Optical Glass, Plastics, Water, Crystal) that concentrates or disperses light rays when passed through them by refraction.

12. A ray of light passes from water to glass. It bends: [RRB Group D 18/09/2018 (Morning)]

Correct Answer: (c) towards the normal and slows down
Solution:

towards the normal and slows down. A ray of light traveling from a rarer medium to a denser medium slows down and bends towards the normal. When it travels from a denser medium to a rarer medium, it speeds up and bends away from the normal.

13. Bifocal lenses are used by people suffering from ________ . [RRB Group D 18/09/2018 (Afternoon)]

Correct Answer: (a) Myopia and Hypermetropia
Solution:

Myopia and Hypermetropia. Bifocal lenses feature two lens powers to help see objects at all distances. Myopia (Nearsightedness) - A condition in which close objects appear clearly, but far ones don't. The image of a distant object is formed in front of the retina and not at the retina itself. Concave lens is used to correct it. Hypermetropia (Farsightedness) - A vision condition in which nearby objects look blurry. The image of a nearby object is formed behind the retina. Convex lens is used to correct it.

14. Clouds looking white in colour are due to the phenomenon of _______ . [RRB Group D 18/09/2018 (Afternoon)]

Correct Answer: (b) Scattering of light
Solution:

Scattering of light - The phenomenon in which light rays deviate from their original path upon striking atmospheric particles. When air molecules scatter sunlight, the cloud's water droplets reflect all colors, resulting in white appearance.

15. Dentists use a concave mirror because the reflection created on it is __________ . [RRB Group D 18/09/2018 (Evening)]

Correct Answer: (d) Virtual and large
Solution:

Virtual and large. Concave mirrors are used by dentists to see a magnified image of a tooth.

16. An object is placed in front of a concave mirror at a point lying between its focal point and center of curvature. The image created will be : [RRB Group D 19/09/2018 (Morning)]

Correct Answer: (b) real and inverted
Solution:

Real and inverted. If an object is placed between focus (F) and center of curvature (C) then the image will form beyond center of curvature and the size of image will be diminished.

17. When a ray of light travels from a denser medium to a rarer medium, the ray will: [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (d) Speed up and bend away from the normal
Solution:

Speed up and bend away from the normal. Snell's laws of refraction of light: The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.

18. The magnification of the mirror for virtual and erect image should be: [RRB Group D 19/09/2018 (Evening)]

Correct Answer: (d) positive
Solution:

Positive. In both concave and convex mirrors, the magnification of a mirror in case of a simulated and erect image is positive.

19. What is the position of the image formed by a concave mirror when the object is placed at the centre of curvature of that spherical mirror? [RRB Group D 20/09/2018 (Afternoon)]

Correct Answer: (d) At the centre of curvature
Solution:

At the center of curvature. Image Formation in Concave Mirror - Between Pole and Focus (Behind the mirror), At the Focus (At Infinity), Between Focus and Centre of Curvature (Beyond the Centre of Curvature), Beyond the Centre of curvature (between center of curvature and focus), At Infinity (At focus).

20. The size of the image formed by a converging mirror when the object is placed at principal focus is ______. [RRB Group D 22/09/2018 (Morning)]

Correct Answer: (c) highly magnified
Solution:

highly magnified. In this case, the reflected rays will become parallel to each other so these rays cannot intersect each other and the image will be formed at infinity. The image formed in this case will be highly magnified, real and inverted.